Stock material or miscellaneous articles – Layer or component removable to expose adhesive – Release layer
Reexamination Certificate
1999-08-26
2001-07-03
Ball, Michael W. (Department: 1733)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
Release layer
C428S345000, C428S3550EP, C522S031000, C522S066000, C522S109000, C522S111000, C522S170000, C156S275700, C156S330000
Reexamination Certificate
active
06254954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive tape with improved room temperature handleability comprising at least one adhesive layer with at least one exposed surface and optionally a backing, wherein the pressure-sensitive adhesive layer comprises an epoxy/polyester based pressure-sensitive adhesive which is crosslinkable upon exposure to actinic or e-beam irradiation. The invention furthermore refers to a method of bonding a first substrate to a second substrate by using such pressure-sensitive adhesive tape and to the assembly prepared by such method.
2. Description of the Related Art
U.S. Pat. No. 4,920,182 describes UV-activatable curable compositions comprising one or more epoxy resins having an average of at least two 1,2-epoxy groups per molecule, one or more flexible polyesters which are terminated by, on average, at least two carboxyl groups, and a metallocene complex initiator. The composition, which can be used for the production of surface coatings on a variety of substrates or as an adhesive, can be cured by the application of heat or with a combination of irradiation and heat. The curing temperature is generally 40-200° C., preferably 80-110° C.
U.S. Pat. No. 4,256,828 describes photocopolymerizable compositions which contain epoxides, organic material with hydroxyl functionality such as hydroxyl-terminated polyesters, and a photosensitive aromatic sulfonium or iodonium salt of a halogen-containing complex ion. The compositions can be used in a variety of applications, for example, as photocurable ink vehicles, binders for abrasive particles, paints, adhesives, coatings for lithographic and relief printing plates, protective coatings for metals, wood, etc. The compositions are typically coated onto the respective surface, and are photocurable at room temperature or below.
The curable hot melt compositions of European Patent Publication No. 0,620,259 comprise an epoxy component, a polyester component, a photoinitiator and optionally a hydroxyl-containing material. The hot melt compositions, which can be tacky or non-tacky, may be applied to a variety of substrates by extruding, spraying, gravure printing or coating (e.g. by using a coating die, a heated knife blade coater, a roll coater or a reverse roll coater). The hot melt composition may also be applied as an uncured, free-standing adhesive film which, when used to bond a first substrate, may be irradiated on one or both sides and then placed between two substrates by the use of heat, pressure or both heat and pressure to bond the film to the two substrates. Alternatively, it is possible to laminate the hot melt adhesive film to a backing at room temperature using a pressure of, for example, 10 psi as is suggested in U.S. Pat. No. 5,436,063. This reference describes a coated abrasive article comprising a backing, a first binder on the backing, a plurality of abrasive particles in the first binder, and a second binder over the first binder and the abrasive particles. The first binder is a photocurable hot-melt adhesive as described in European Patent Publication No. 0,620,259.
While the crosslinkable hot melt epoxy/polyester based adhesives described above have broad utility, there are certain, specific applications where improved mechanical integrity and/or cohesive strength are desired or required. Therefore there is a need for a crosslinkable epoxy/polyester based pressure-sensitive adhesive materials available to the person skilled in the art to allow him or her to select appropriate adhesive materials exhibiting advantageous properties for a specific application and, in particular, for the preparation of unsupported and supported pressure-sensitive adhesive tapes with improved and/or convenient handleability at room temperature or below. Other objects of the present invention can be taken from the detailed specification below.
BRIEF DESCRIPTION OF THE INVENTION
The present invention refers to a pressure-sensitive adhesive tape with improved room temperature handleabilty comprising at least one pressure-sensitive adhesive layer with at least one exposed surface and optionally a backing, wherein the pressure-sensitive adhesive layer comprises an epoxy/polyester based pressure sensitive adhesive which is crosslinkable upon exposure to actinic or e-beam irradiation and which comprises:
(i) 30-80% by weight of a polyester component comprising one or more amorphous polyester compounds;
(ii) 20-70% by weight of an epoxy component comprising one or more epoxy resins and/or monomers;
(iii) 0-50% by weight of a hydroxyl-functional component containing one or more hydroxyl-containing compounds having a hydroxyl functionality of at least 1; and
(iv) an effective amount of a photoinitiator component for crosslinking the pressure-sensitive adhesive;
wherein the weight percentages refer to the total mass of components (i)-(iv) and add up to 100% by weight, and further wherein the pressure-sensitive adhesive which exhibits a holding power of at least 5 minutes.
The present invention furthermore refers to a method of bonding a first substrate to a second substrate with a pressure-sensitive adhesive tape according to the invention having two exposed adhesive surfaces. The method comprises the steps of applying the first exposed surface of the pressure-sensitive adhesive to the first substrate and attaching the second substrate to the second exposed surface of the pressure-sensitive adhesive whereby the pressure-sensitive adhesive layer according to the invention is subjected to actinic or e-beam irradiation and, optionally, heat prior to bonding them to the respective substrate within the after-cure bonding time or after bonding them to the respective substrates. The invention furthermore refers to assemblies which are obtainable by such method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The term pressure-sensitive adhesive tape as referred to above and below describes supported or unsupported, essentially two-dimensional articles such as sheets, strips, ribbons or die-cut parts (i.e., the extension of the articles in two directions distinctly exceeds the extension in the third direction):
(i) which are tacky at room temperature and can be applied to a wide variety of substrates by exerting, for example, finger pressure, and
(ii) which can be conveniently handled at lower temperatures such as room temperature without breaking, i.e., which exhibit a sufficiently high internal strength and cohesivity and a certain elasticity so that removable liners can easily be stripped off the tape without damaging the tape, and the tape can at least be slightly stretched and transferred to the substrate by hand.
Feature (i) requires an initial 90° peel adhesion value on stainless steel as measured 20 minutes after application onto the substrate according to the test method specified below of at least 4N/inch or more.
Feature (ii) requires a holding power time as measured according to the test method specified in the experimental part below, of at least 5 minutes or more.
The epoxy/polyester based presssure-sensitive adhesive tapes according to the present invention are crosslinkable and can be converted to crosslinked pressure-sensitive adhesive tapes upon exposure to actinic or e-beam irradiation and, optionally, heat. The crosslinked pressure-sensitive adhesive may bond, for example, 2 substrates, and the resulting configuration is termed as an assembly.
The term adhesive film as referred to above and below describes two-dimensional articles which may be tacky or non-tacky at room temperature and exhibit a debonding time of less than 5 min. and, in particular, of not more than 3 minutes.
The pressure-sensitive adhesive tapes of the present invention which may be supported or unsupported, exhibit at least one pressure-sensitive adhesive layer comprising an epoxy/polyester based pressure-sensitive adhesive.
It was found by the present inventors that for imparting improved room temperature handleability to the pressure-sensitive adhesive tapes it is essential
Bennett Greggory S.
George Clayton A.
Hitschmann Guido
Lamon Alain H.
3M Innovative Properties Company
Ball Michael W.
Knecht III Harold C.
Tolin Michael A.
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